import { mathFloor } from './constants';
import { distance as v2Distance } from './vector_util';
/**
 * Catmull-Rom spline 插值折线
 * @author pissang (https://www.github.com/pissang)
 *         Kener (@Kener-林峰, kener.linfeng@gmail.com)
 *         errorrik (errorrik@gmail.com)
 */

/**
 * @inner
 */
function interpolate(p0, p1, p2, p3, t, t2, t3) {
  let v0 = (p2 - p0) * 0.5;
  let v1 = (p3 - p1) * 0.5;
  return (2 * (p1 - p2) + v0 + v1) * t3 + (-3 * (p1 - p2) - 2 * v0 - v1) * t2 + v0 * t + p1;
}

/**
 * @alias smoothSpline
 * @param {Array} points 线段顶点数组
 * @param {Boolean} isLoop
 * @return {Array}
 */
export default function (points, isLoop) {
  let len = points.length;
  let ret = [];
  let i = 0;

  let distance = 0;
  for (i = 1; i < len; i++) {
    distance += v2Distance(points[i - 1], points[i]);
  }

  let segs = distance / 2;
  segs = segs < len ? len : segs;
  for (i = 0; i < segs; i++) {
    let pos = (i / (segs - 1)) * (isLoop ? len : len - 1);
    let idx = mathFloor(pos);

    let w = pos - idx;

    let p0;
    let p1 = points[idx % len];
    let p2;
    let p3;
    if (!isLoop) {
      p0 = points[idx === 0 ? idx : idx - 1];
      p2 = points[idx > len - 2 ? len - 1 : idx + 1];
      p3 = points[idx > len - 3 ? len - 1 : idx + 2];
    } else {
      p0 = points[(idx - 1 + len) % len];
      p2 = points[(idx + 1) % len];
      p3 = points[(idx + 2) % len];
    }

    let w2 = w * w;
    let w3 = w * w2;

    ret.push([interpolate(p0[0], p1[0], p2[0], p3[0], w, w2, w3), interpolate(p0[1], p1[1], p2[1], p3[1], w, w2, w3)]);
  }
  return ret;
}
